Furnace for burning coal-screenings



(No Model.)

P. LpBARTLETT. FURNACE FOR BURNING COAL SCREENINGS No. 493,854-.

Patented Mar; 21, 1893.

wi p ss y tempts at burning such coals with a heavy 30,

UNITED STATES PATENT OFFlCEe FRANK L. BARTLETT, OF PORTLANDpMAINE.

FURNACE FOR BURNING COAL-SCREENINGS.

SPECIFICATION formiug part of Letters Patent No. 493,854, dated March21, 1893.

Application filed March 25, 1892.

.To all whom it may ooncern:

Be it known that I, FRANK L. BARTLETT, a citizen of the United States,residing at Portland, in the county of Cumberland and State of Maine,have invented certain new and useful Improvements in Furnaces forBurning Coal-Screenings; and I do hereby declare the following to be afull, clear, and exact descri ption of the invention, such as willenable others skilled in the art to which it appertains to make and usethe same. e

The objectof ny invention is to provide means for burning finelypulverized Waste coal under stean boilers and other furnaces. Waste coalfrom anthracite mines has heretofore been burned by mixing the fine coalwith sawdust, spent tan bark or with bituminous coals. The problem ofburning the waste from the soft lignite coals, such as are mined inColorado, YVyoning, New Mexico and other Western States, has never beensatisfactorily solved so far as I am aware. Such waste is extremelyfine, fully one half being dust and often an impalpable powder,so thatany device such as is economically used on the heavier and more densecoal slack of the Eastern or Middle States, fails to work on the lighterlignite coals of the Western States. All atblast, results in filling theflues of the boiler and the conduits of the furnace with fine halfburned coal, or else when the blast is lightened the grates are packedwith the fine coal so that the air cannot force its way through. Again,no method has been found, so far as I know, for burning the dense Volumeof smoke which such coal gives off.

The object of the present invention is to overcome the difficultiesmentioned and to efiect the complete and economical combustion of thiskind of coal dust without filling the flues with dust, without theproduction of smoke and without destroying the grates and the walls ofthe furnace.

The various features of my invention will be described in thespecification and set forth in the claims.

In the accompanying drawings, I illustrate my invention as applied to ahorizontal tubular boiler.

Serial No. 426.330. (No model.)

In the drawings Figure l is a central longitudinal section. Fig. 2 is across section, half being on line :r w and half on the line y y ofFig. 1. Fig. 3 is a perspective view of one of the hollow perforatedbrick used in the bridge wall, and. Fig. 4: is a section through thesame. v

A represents the stean boiler and B is a perforated inclined grate whichI prefer to make of solid cast bars having one-fourth inch perforations.

C is the bridge wall which in this case extends the entire distanceacross the furnace and is made hollow to admit the blast 'which entersthrough the pipe L. This pipe as herein shown is connected with a blowerP. The top of the bridge wall, as herein shown, is arched and itcontains on each side of the arch a row of perforations d adaptedto'discharge a hot air blast obliquely toward the front and rear of thefurnace. These perforations d are formed in hollow bricks D pret erablyof cast iron which are-set in the brick Work of the arch. The inneredgeof the brick D is open and allows the air to pass through theperforations.

In the front partitio of the bridge wall is an opening for admitting airbeneath the grate. I prefer to use for this opening a pipe E which isfixed in the lower part of the Wall and points obliquely upward. Thisopening is controlled by a damper F which is opened and closed by meansof a rod G. In rear of the bridge wall is an inclined surface H wherethe ashes collect as they come over the bridge wall and in rear of thisis the ash collecting clamber I.

N is the ash door. p

K represents the stack and J is the damper which controls the draft inthe stack.

In Operating the furnace a light blast 'from a fan or other device isdelivered into the hollow bridge Wall at a low pressure, say two ouncesto the square inch. The air will pass out of the' perforations d d inthe top of the wall as a hot blast, being heated in its passage 5 Thecolder air will A fire havthrougl the bridge wall. be discharged throughthe pipe.

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, The backward direction of the cold blast issuing from the pipe Ebeneath the grate and the hot blast through the front row of holes d dtend to hold back the smoke and light dust from the coal giving it arotary motion, while the s'tack Ic tends to draw it slowly forward andthrough the flues of the boiler. The result is that the coal is burnedin passing over the perforated bridge wall and meeting the heated aircurrents from the openings d d and the fine completely burned ash dropsin the ash chamber I, accumulating at the bottom of the inclne II whereit nay readily be removed through the ash door N( It will be observedthat the chamber I growsgradually larger from the bridge wall backwardto the rear erd of the boiler. This coustruction of the apparatus is ofgreat importance for the reason that the combustion of the dust beginsin the vicinity of the bridge wall and as it proceeds it requires anexpanding chamber or flue in which to effect a complete combustion andto prevent counter currents. The fiue grows graduaily larger as theVolume of gas caused by the combustion of the dust expands.

In practice the light clinker which forms on the grate is not disturbedfor several hours, the fuel being frequently spread over the hotclinkerthus formed, and burned ofi until the porous clinker has becometoo thick to allow the blast to penetrate, when it is broken up andremoved.

It will be seen that the operation of this invention is nearly thereverse of ordinary firing,inasmuch as the finecoal is burned in the airand the ash deposited in the rear of the boiler instead of under thegrates as is customary. By means of the cold blast under the grates andthe hot blast through the perforations of the bridge wall, completecombustion is not only Secured, but the grates last much longer and thewear on the boiler and furnace is lessened, the smoke ceases to be anuisance, the flues do not fill up and a very cheap and hithertounutilized class of fuel can be burned. -For effective work underboilers and stills it is found necessary to have &93,854

the grate quite near the boiler to be heated, much nearer in fact thanis customary with ordinary firing.

When this invention is applied to furnaces already set in the usual way,the rear ends of the grate are raised and a fire brick arch 'M turned atthe front end near the charging door. The object of this arch is toprevent the cold air from the lower blast from passing through andimpinging on the cooler surface of the boiler plates and thus reducingthe temperature of the blast below the point of combustion. This deviceis not necessary when the grate is constructed to be within say eighteenor twenty inches.

I claim- 1. In a furnace for stean boilers and other like purposes, theconbination of a perforated grate, a lollow bridge wall forn'ing an airchamber, perforations at the top of said bridge Wall for supplyinga hotblast from the upper part of said air chamber, an opening through thelower portion of said bridge wall beneath said grate for discharging thecooler air from said air chamber, substantially as described.

2. The herein described method of burning fine coal under stean boilersconsisting of Spreading the coal in a thin layer over a perforatedgrate, forcing an air blast beneath said grate sufficient 'to lift thefine coal dust from said grate, blowing jets of heated air into theSuspended coal dust immediately after it leaves said grate and burningit while held in suspension, and slowly drawing off the products ofcombustion through the stack, substantiall y as described.

3. In a furnace for steam boilers and other like purposes, thecombination of a finely perforated grate, an air blast apparatus fordelivering air under pressure beneath said grate, a bridge wall havingair discharge openings therein and a gradualiy enlarging or expandingchamber in rear of said bridge wall extending without substantialdiminution of section to the rear of the furnace, substantially asdescribed.

In testimony whereof I affix my signature in presence of two witnesses.

FRANK L. BARTLETT. VVitnesses:

HENRY LLOYD, FRANK MCFARLANE.

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